Drop the Aura of decay. IT sounds great in theory until it takes a 5+ to hurt guardsmen, yes it will wound when you get there but more often then not you could get other better options for the points. I would take Breath of Chaos or Demonic gaze before I got it on the Demon princes. Also drop the icons. If you must take it in first wave only. You want to load up your first wave with the fatties if Epidemius doesn't come out while kills happen doesn't count so you just have to maximize your first wave and hope to get it. IF you gonna keep masque then I would definetely take breath of chaos. Something like this:

GUO or 2 heralds of nurgle with BoC
Masque or Herald of nurgle with BoC
Epidemius

Beasts
Beasts
Beasts-Usually I take them in small units and max the elite choice depending on points also running them as monats ups your first wave

Plaguebearers-1 large group to hide epidemius in and if you must take a Icon put it here
Plaguebearers-10ish
Plagueberers-10ish
Nurglings-6ish
Nugrlings-6ish

Demonprince of nurgle/IH/Wings/Breath of Chaos x3
I don't take any upgrades such as Noxious touch as its part of the tally and with this set-up you can have the tally potentially maxed out turn one. Thats 6 breath of chaos. Also a reason I don't recomment the Aura of Decay is once the demon princes drop they are gonna be huge targets and usually won't make much use of the upgrade more then once. Also the BoC gives you a 50/50 chance of glancing a vehicle which could be great allowing you a chance to make it not move and then get free hits on it next turn.